Silencer for compressible fluid devices



Nov. 1, 1960 R. M. GREFF 2,958,387

sILENcER FOR coMPREssIBLE FLUID DEVICES Filed sept. 29, 1955 SILENCER FOR COMPRESSIBLE FLUID DEVICES Richard M. Greif, Royal Oak, Mich., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Sept. 29, 1955, Ser. No. 537,479

1 Claim. (Cl. 181-42) is usually accompanied by a considerable amount of Y undesirable noise, especially as the rate of delivery increases to a value near the rated capacity. This noise is caused by disturbances in the path of fluid movement and is usually comprised of acoustic disturbances having a wide frequency range. Such noise is commonly termed white noise since it is comprised of disturbances of almost every frequency in the audible range with none of the frequencies being predominant. In addition to this so-called background noise, there may also vbe a predominant pitch of a given frequency and at least one other negligible pitch of a different frequency. These latter disturbances may be detected in most cases by ear and when the pitch frequencies of the same are measured by a suitable audio-oscillator pickup, it is usually found that one frequency will be an even multiple of the other, typical values being 500 c.p.s., 1,000 c.p.s., 1,500 c.p.s. etc.

Various forms of silencers have been employed for reducing the noise intensity but their installation is usually accompanied by a significant total pressure drop in the delivery air stream and by a reduced operating efficiency of the fluid machinery. When such silencers of known construction are used with high temperature gases, the useful life of the same is reduced by reason of the accelerated rate of corrosion or oxidation. The majority of these silencers of known construction make use of the sound absorption principle wherein a suitable sound absorbing medium is interposed in the air delivery path thereby causing the energy of the sound waves to become dissipated as heat with a resulting decrease in sound intensity. The operation of other types of silencers sometimes employed in the art is based upon the principle of sound wave cancellation wherein the sound waves of Va given frequency are attenuated by another sound wave of an identical frequency in certain regions while the sound waves in other adjacent regions are amplified in intensity, the total energy of the resulting acoustical disturbance and the frequency of the same remaining unchanged. These latter silencers are effective only in specific applications where a reduction'in sound intensity in certain specified regions is desire to the exclusion of other regions.

The silencer of my instant invention employs the sound absorption principle above defined, and it is capable of reducing the noise intensity in apparatus of the type above mentioned by converting into heat the energy of the sound waves at all frequencies in the audible range including those frequencies of both predominant and negligible pitch.

According to a principal feature of my instant inven- Patented Nov. l, 1960 tion, I have provided a silencer structure which forms little or no obstruction to the moving air stream and which is characterized by a body of sound absorbing material situated adjacent the path of air movement. Means are provided for `distributing the energy ofthe individual sound waves throughout a large portion of the sound absorbing material as distinguished from only that isolated portion in the immediate vicinity of the sound wave thereby facilitating the above-mentioned energy Yconversion.`

The provision of an improved silencer of the type above referred to being a principal object of my instant invention, it is a further object of my invention to provide a silencer of simplified construction which may be readily adapted to be used with a large variety of high velocity air delivery devices with a minimum amount of alteration. v

It is another 4object of my invention to provide an improved silencer of the type above described wherein the principle of sound absorption is employed and wherein provision is made for amplifying the degree of sound absorption for -a specified area of the sound absorbing medium.

Another object of my invention is to provide a silencer for a high velocity air delivery conduit means which is capable of reducing the intensity of the noise accompanying the air delivery and which is character ized by a negligible pressure drop in the fluid path.

Other objects and features of my instant invention will readily become apparent from the following description.

For the purpose of illustrating one preferred embodiment of my invention and a structural environment for the same, I have shown an air blower for use with a military tank turret to ventilate the tank operators compartment. Hon/ever, it will be understood that the principles of my invention may be applied to other types of blowers used in other installations and in other types of uid machinery; For example, the silencer herein disclosed may be readily adapted to be installed on either the inlet or the outlet side of a compressor used with a gas turbine power plant for absorbing sound waves of blade frequencies.

For the purpose of particularly describing the features of my invention, 'reference will be made to the accompanying -drawings wherein:

Figure 1 shows a schematic elevation view of a military tank having a turret with a ventilator blower suit ably positioned for forcing cool air from the exterior of the turret into the operators compartment;

Figure 2 is an enlarged sectional View of a portion of the turret illustrated i-n Figure l showing the blower with the silencer of my instant invention secured to the outlet side thereof; and

. Figure 3 is a cross sectional view of the silencer of Figure 2 and is taken along section line 3 3 of Figure 2.

VReferring first to Figure 1, numeral 10 is used to designate the tank turret which is rotatably supported on the tank chassis structure 12, ldefines an interior operators compartment and the tank propulsion mechanism comprises a driving sprocket 14, a forward idler structure 1-6, and intermediate idler wheels 18. A plurality of wheels 20 is carried by the chassis structure 12 for supporting the tank, each wheel 20 forming a portion of an independent resilient suspension.

The turret 10 includes `an access opening 22 and a forward opening 24 through which a cannon 26 may be projected. The rearward portion of the turret 10 is formed with an opening 28 within which is secured an air blower 30, the intake side of the blower 30 communicating with the exterior of the turret to accommodate the introduction of air to the interior.

'Y Referring next to Figure 2, the blower 30 may becomprised of an outer cylindrical shell 32 having a peripheral flange 34 which may ybe bolted to the periphery of the turret opening 28, suitable bolts 36 being provided for this purpose. The rotor may be powered by an electric motor generally shown at 38 and suitable bracket structure may be provided for rigidly connecting the motor stator 38 to the cylindrical shell 32. An electrical connection is generally designated by numeral 40 -and is connected to the motor 38 for energizing the same.

The blower 30 is adapted to force air in a downward direction, as viewed in Figure 2, and the discharge end of the blower may be formed with a suit-able groove 42 for the purpose of retaining the blower silencer of my instant invention which will now be described.

The silencer of my instant invention is designated in Figures 2 and 3 by numeral 44 and it is comprised of an outer shell 46 which may be cylindrical in shape and which is formed at the upper end thereof with an inwardly directed flange 48. The flange 48 may overlap a supporting ring 50 having a collar 52 surrounding the discharge end of the blower casing 32. Another cylindrical shell 54 may be situated within the shell 46 in concentric relationship therewith and the upper end of the shell 54, as viewed in Figure 2, extends upwardly and may be received within the collar 52. The collar -2 and the upper end of the shell 54 may be clamped into engagement with the casing 32. A peripheral recess is formed in the collar 52 and in the upper end of the shell 54 for the purpose of registering with the groove 4Z to retain the concentric shells 54 and 46 securely in place. I prefer to use a clamping band 55 of known construction for the purpose of applying a clamping force to the collar 52. A rubberized insulating strip 53 may encircle the end of the cylindrical shell 32 under the collar 52.

An annular end plate 56 may be secured to the lower ends of the concentric shells 54 and 46 and it may be secured in place by suitable fastening means such as rivets or bolts 58. The inner shell 54 is formed with perforations 60 throughout substantially its entire area land opening into the -annular space defined by the concentric shells 54 and 46. This annular space is filled with loose fibrous material 62 such as glass fiber insulating material. By preference, the glass fiber should be packed with relatively high density and although I contemplate that fiber diameters of varying magnitude may be employed I have found that a fiber diameter of .0017 with a tolerance of -l-.00003 and .000'02 is quite successful. Also it is preferred to provide a glass fiber density of 3 lbs. per cu. ft. with a tolerance of approximately i%.

The annular chamber defined by the concentric shells or shrouds 54 and 46 may be divided into two sections by an aluminum foil septum 64, this septum being cylindrical in shape and concentrically arranged with respect to the shells 54 and 46. The axial length of the septum 64 is preferably equal to the distance between supporting ring 50 and end plate 56. By preference, the distance between the septum 64 and the shell 54 is about one-half the distance between the septum 64 and the shell 46, but this relationship may be altered in order to suit a particular design requirement. rIhe septum 64 is preferably formed of aluminum foil with a thickness of .001 and an adhesive may be used to adhere the adjacent glass fiber fibers to either side of the aluminum foil. One adhesive suitable for this purpose is phenol formaldehyde which is capable of resisting breakdown due to exposure to the air passing through the inner shroud.

During operation, the discharge from the blower 30 passes axially through the inner shell 54 and the sound waves accompanying this ow may pass through the perforations in the shell 54 and become absorbed in the'fibers of the glass yfiber packing 62. The energy of the sound waves causes the fibers of the glass fiber material to vibrate thereby causing the energy to become dissipated in the form of heat with a resulting decrease in the intensity of the sound waves within the audible range including the predominant and the negligible pitch above discussed. The aluminum foil 64 is caused to vibrate with minute forced vibrations as the acoustical disturbances in the moving medium come in contact therewith. The sound waves 4exist throughout the entire medium and yare comprised of pressure disturbances capable of exerting a pressure differential across the aluminum foil in a given location and this in turn causes adjacent areas of the foil to vibrate. The vibration of the foil in this manner causes the fibers -of the packing throughout substantially the entire blanket to vibrate by reason of the intimate contact between the aluminum foil and the adjacent fibers. The adhesive which lbinds the foil to the adjacent fibers increases this tendency and magnifies the degree of absorption of the energy of the sound waves.

The foil septum is therefore effective to facilitate the dissipation of theY energy of each individual sound wave throughout the entire body of the insulating fibers rather than throughout only a localized portion of the same.

Although I have particularly described one preferred embodiment of my invention, I contemplate that many variations thereto may be made without departing from the scope of the invention as defined by the following claim.

I claim:

In combination, a casing having an annular retaining groove adjacent the lower end thereof, a silencer for attachment to said casing comprising, an outer shell having a substantially larger diameter than said casing, said outer shell defining an inwardly directed flange at its upper end, a ring for supporting said silencer on said casing defining an outwardly extending flange portion and an upwardly extending integral collar, said outwardly extending flange adapted to lie under said inwardly directed flange on said outer shell, said collar adapted to encircle said casing, there being a peripheral recess formed in said collar adapted to register with said groove in said casing, an inner perforated shell having a diameter slightly larger than said casing and disposed in concentric relationship within said outer shell, said inner shell extending upwardly to a distance fiush with the top of said collar, a rubberized insulating strip adapted to encircle the end of said inner shell and disposed between said inner shell and said casing, la clamping band adapted to encircle said collar for clamping said collar, said inner shell and said rubberized strip into said retaining groove, a septum disposed in coaxial relationship between said outer and said inner shells whereby separate chambers are formed therebetween, said chambers being filled with insulating material, and an annular end plate secured to the lower end of said shells adapted to close said separate chambers.

References Cited in the file of this patent UNITED STATES PATENTS 722,567 Crawford Mar. 10, 1903 869,868 Spencer Oct. 29, 1907 1,115,873 Spencer Nov. 3, 1914 1,941,222 Pew et al. Dec. 26, 1933 2,073,951 Servais Mar. 16, 1937 2,081,953 Perry June l, 1937 2,089,492 Lambert Aug. 10, 1937 2,177,393 Parkinson Oct. 24, 1939 2,270,825 Parkinson et al. Jan. 20, 1942 2,273,092 Dole Feb. 17, 1942 2,363,068 Leadbetter Nov. 21, 1944 2,543,461 Latulippe Feb. 27, 1951 2,674,336 Lernmerman Apr. 6, 1954 2,741,498 Elliott Apr. 10, 1956 2,785,099 Holtsford Mar. 12, 1957 

